Found the Audio Nirvana website, a sprawling eyesore of a site (sorry Audio Nirvana, if you are reading...) &came across these opinions they expressed there, e.g.
On Cabinet Material:
" Plywoods will generally give a softer sound, particle board--intermediate, MDF will give the most detail. For a soft listening room, you may prefer MDF. Medium rooms--particle board. And for live rooms, we recommend high quality Baltic Birch or marine plywood. As the quality of your source material goes up, so too can the density of the material you use to make your cabinets"

And a fairly long exposition criticizing the 'bass horn' design, and praising the bass reflex design. (newbie here wonders if bass horn is same as TL?)
which I won't copy paste here since it is very long.

I would not pay attention to what David Dicks says. He doesn't really know much about box design. I've had to fix a number of his boxes to work properly.

He also can't take constructive criticism. He had a major hissy fit when people here critiqued his work, and got himself banned.

The comment about box material is opposite of what we have found to be true. The problem with MDF is that is it stores energy and then oozes out more or less continuous time-smeared low level grunge that buries the low level detail.

Some of the drivers are considered good, the ones i had or heard were not (bit you can't buy any of those any more). Some of them cannot be made to go very low either.

A bit more technical way to think about it is that the higher the system Q, the lower its HF mass corner [Fh = 2*Fs/Qts], the lower the cab's stiffness and the greater its mass is required to help damp it, ergo until it gets to a > 0.707 Qt, there's no such thing as too stiff a cab, just a point of diminishing returns as the Fh goes down.

From this it becomes obvious that in general, MDF is only really practical for mids - up cab construction and PB and other lossy materials are only good for extremely high Qt systems.

That, or push the cab's Fs down to below its LF mass corner [Fl = Fs*Qts/2], requiring concrete bunker or similar massive construction for sub systems as even some building/home construction isn't massive enough as I found out the hard way.

In short, for a typical sealed, vented alignment one ideally wants a cab with a Fs > ~1.56x the system's HF mass corner, so that there's not enough acoustical energy [eigenmodes, reflections] bouncing around inside to excite it, with 3/4" [18-19 mm] no-void plywood being the accepted woodworking 'standard' [around here anyway] combined with some bracing to tie all sides together to keep it from potentially 'breathing'.

GM

__________________Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.

Oh for some CRS or aluminium. Mind, given the amount of damage I can cause with a hammer, best not to think about arc welders & angle grinders.

As for the views on AN's site, it's been a while since I looked at it, but as I recall, since they were regularly plonking drivers into cabinets which resulted in some downright horrific alignments, I would be a trifle cautious. They have also launched a 'horn' series of drivers, suggesting that they have changed their mind on this matter. Still, I've dug it out of their site & will offer a few thoughts. To keep the size down, I've just copied their numbered claims rather than the short paragraph of text under each -if anybody wants to look at it, you'll find it here: DIY Loudspeakers. Loudspeaker kits. Full range loudspeakers. Audio Nirvana, Lowther, Fostex. Vacuum Tube Amplifiers For Sale Granted, I may be considered as biased since I've designed quite a few back-horns, but I design other types as well & what I'll put is simply the technical / physical reality.

Quote:

1. Distortion is created by reflections from the 'box' behind the speaker.

It can be, in a badly designed one. This matter depends on the size & shape of the low-pass chamber, and whether it is appropriately damped, i.e. has been lined / stuffed to attenuate early reflections. This is not rocket science, just straightforward acoustic engineering / testing.

Quote:

2. Horn-loaded designs tend to 'fatten' or 'smear' the midrange and upper bass regions of the music.

Group delay (which they are presumably referring to) can be an issue if a back-horn is run too high in frequency; back-loaded horns are only useful over a relatively narrow BW, same as any back-loaded cabinet, so you need to have a reasonable acoustic low-pass built into the design. Ideally you want the horn to roll off 2nd or 3rd order above the mass corner (Fhm) assuming this is below about 300Hz once actual system Q (driver & any series R from wire or amplifier output impedance) is factored in. If not, you either have to roll it off anyway & accept a hole in the response between the horn's upper corner & the driver's mass corner, or go compound, with a short midrange horn 'filling in' that region. In general, it's not difficult, the main issue to contend with being the myth that a low driver Q is necessary for use in back horns. In reality, you want a driver with parameters that would suit it to BRs -the only catch in that being that it needs sufficient motor power to drive the horn without stalling out. That can be accounted for. Which is a long-winded way of saying -same as 1/ i.e. it should only be an issue for poorly designed ones

Quote:

3. Stereo imaging and soundstage are very poor with bass horn designs

It can be an issue in bass horns that have been run up too high in frequency, resulting in excessive group delay in the lower midrange, but a blanket statement of this kind without any context or caveats is incorrect in terms of both physics & engineering

Quote:

4. Horn-loaded cabinets exhibit a ragged bass response.

Drivel. That is a matter dependent on the size of the horn in question, what it's QW cutoff F0 and impedance matched corner frequency Fc are, and what boundary loading it is intended for. If a horn is significantly undersized / compromised (i.e. it's QW tuning frequency is significantly lower than the frequency it is impedance matched down to, which is a function of terminus size) then it will have an issue with standing waves, which can be partly addressed / compensated for in the design stages. Most back horns are compromised to some degree due to the sheer size involved, but that does not mean every single bass horn has a ragged output. To put it mildly, that is a sweeping and technically inaccurate claim.

Quote:

5. Horn-loaded cabinets do not play very low bass.

Another statement that is completely incorrect on a technical level. As anybody who has heard, say, a BIB pipe-horn will rapidly confirm. In fact, the reverse is the case. If you've the room, you can actually get rather more LF extension out of a driver in a bass horn than you can in a reflex box (although there can be caveats to that).

Quote:

6. Horn-loaded cabinets are very difficult and expensive to build, and hard to place in most rooms.

Nope. The BIB for instance has a total of 6 panels, same as a BR -arguably less, since its internal baffle serves as bracing, which a moderate - large BR enclosure will almost certainly need. Otherwise -depends on the design. They do not necessarily have to be either difficult, nor expensive to build. FH3 is another popular example -few builders have had serious problems, even inexperienced woodworkers. The Fostex factory designs, many of those by Nagaoka-san, and some of my own have a fair few parts, as do many of my own, but it's all 90 degree angles & butt-joints, so while it may take a little longer, if you can use a tape measure, it's not actually difficult.

Quote:

7. There is no significant efficiency advantage with the bass horn designs.

As far as the physics goes, this is a completely incorrect statement. You can get a whole lot more gain, across a significantly wider BW with a bass horn than it's BR cousin. However: back horns as noted are only useful over a relatively narrow range; they do not operate over the entire frequency region. So in practical terms, system sensitivity is determined by the driver's inherent sensitivity / FR. As a rule, when in doubt, better to design the horn to have an excess of gain & damp out what you don't need.

Quote:

8. It is possible to overdrive bass horns.

It is possible to over-drive most any enclosure. A bass horn, being a more efficient load, actually should provide tighter control over the driver & likely (depends on the design) greater dynamic range, not less.

Quote:

9. Horn Loaded cabinets were never designed to accomodate [sic] full-range speakers.

Never designed by whom, one wonders. Voigt, and a goodly number of W.E. and RCA engineers (Harry Olson for example) might beg to differ. It is also somewhat irrelevant what a first conception may have been, providing performance is good. The Wright brothers didn't conceive jet engines for their aeroplanes -does that mean we should stop using them? CSA mention Klipsch as the inventor of horn loaded speakers in their text, but without taking anything away from him and his deserved status, he did not actually invent bass horns TTBOMK (although he certainly helped popularise them), so you can take that statement for what it's worth.

Thanks for methodically going through those Scottmoose. I totally agree with all your points, and I, actually prefer a bass horn over all other bass means. If you have room or if the design can be folded and made compact - it's almost the ideal source of clean and efficient bass.

What slightly depresses me is that I was only half awake when I wrote the above and while I appear to have got the factual content correct, I wish I could edit some of my grammar, which was not exactly up to standard.

__________________"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.

Hello all. Sorry am late on posting but I have to say my 2 cents worth on A. N. Drivers. I had bought one of the first batchs of 8' s with a steel frame and a phase plug. All of my drivers were defective. I got my money back with out shipping cost. So my respect to Daved Dicks for standing behind his return but I could write a book about other things but, I am not here to bash anyone but share my experience. I would go Fostex Tang Band and then Mark Audio. All the other drivers I cannot afford. Like Lowther or Aer or festrix drivers to name a few. Also with out Dave Chris and all the Planet 10 people I would be lost. Also bud p. And scottamoose and Bob Brian's and Godzilla and John from zaph audio and Humble homemade Hi and audio express magazine. This is a new year so I am starting it off on the right foot. Keep up doing diying everyone it has saved me thousands and I have learned so much. Just getting started. Cheers. Jeff

A bit more technical way to think about it is that the higher the system Q, the lower its HF mass corner [Fh = 2*Fs/Qts], the lower the cab's stiffness and the greater its mass is required to help damp it, ergo until it gets to a > 0.707 Qt, there's no such thing as too stiff a cab, just a point of diminishing returns as the Fh goes down.

From this it becomes obvious that in general, MDF is only really practical for mids - up cab construction and PB and other lossy materials are only good for extremely high Qt systems.

That, or push the cab's Fs down to below its LF mass corner [Fl = Fs*Qts/2], requiring concrete bunker or similar massive construction for sub systems as even some building/home construction isn't massive enough as I found out the hard way.

In short, for a typical sealed, vented alignment one ideally wants a cab with a Fs > ~1.56x the system's HF mass corner, so that there's not enough acoustical energy [eigenmodes, reflections] bouncing around inside to excite it, with 3/4" [18-19 mm] no-void plywood being the accepted woodworking 'standard' [around here anyway] combined with some bracing to tie all sides together to keep it from potentially 'breathing'.

GM

Practically all the math and terminology is lost on me, but from what I misunderstood, the Wilson Audio approach is to push the cab's F down (whatever F is), while you guys found birch ply ideal. Two other cabinet approaches come to mind, one is Michael Green loudspeakers, which uses real wood, wood pulp filling, and some sort of method to tighten the cabinet sides to 'tune' the resonances, and the one used/invented(?) by Lindemann:Lindemann BL-10 Bookshelf Speaker Review | A Unique Audiophile Experience

Audio Note speakers seem to fall more to your camp, being ply cabinet; they sound kinda colored to me, and not worth their price, but then again, what do I know? Might be implementation not necessarily the fault of ply. Heard alot of colored MDF speakers too.